Your question made me curious about this, so I looked it up.* Lincoln's favorite food was chicken fricassee. (Chicken in cream sauce.)* Lincoln said his wife Mary's white almond cake was the best cake he's ever had. (The recipe contains milk and egg whites.)* There was veal on the menu of his second inauguration in 1865. (As well as game and lots of other meat.) Even the salads were chicken, and lobster. They also served 6 flavors of ice cream. (Lots of cranking the ice cream maker in those days.) Just about the only thing a vegan could have had at that even were the fruit ices and coffee.)

***I can't fault Lincoln for not being veg. He was a product of his time, and had more than enough on his plate to deal with with human slavery and the south threatening to secede from the Union. Also they didn't have factory farms then, so farm animals likely had a decent life until killed for food.